JPH0593928A - Organic nonlinear optical material and nonlinear optical device formed by using this material - Google Patents

Abstract

PURPOSE:To provide the org. nonlinear optical material having stable and large nonlinear optical characteristics and to improve its transparency in a visible wavelength region by melting and kneading polyvinylidene fluoride (PVDF) and acrylic polymer and subjecting the mixture to a heat treatment after rapid cooling from a molten state. CONSTITUTION:The growth of the crystal of the PVDF is limited by the acrylic polymer mixed well with the PVDF and the resin compsn. having a low degree of crystallization is obtd. if the PVDF and acrylic polymer mixed at a prescribed ratio are melted with each other by melting and kneading and the resin compsn. of a molten state is rapidly cooled by a cooling medium. The crystallization of the resin compsn. takes place in the presence of the acrylic polymer when the resulted resin compsn. is heat treated. A quadratic nonlinear optically active org. material is introduced into the host polymer (resin compsn.) obtd. in such a manner and is dispersed therein. The nonlinear optically active org. material introduced into the host polymer is uniaxially oriented by an electric field impression method, by which the high-performance nonlinear optical material is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic non-linear optical material and a non-linear optical device such as a wavelength conversion element or a light modulation element using the organic non-linear optical material.

[0002]

2. Description of the Related Art Currently, organic materials are used as nonlinear optical materials.
Materials such as inorganics and semiconductors are being researched and developed. Among these, the advantages of the organic nonlinear optical material are that it has a high response speed and a large nonlinear optical constant.
Taking advantage of this feature, research and development of novel organic nonlinear optical materials and deviceization technology aiming at application to wavelength conversion second harmonic generation element (SHG (Second Harmonic Generation) element) and electro-optical modulation element Is being researched and developed.

Of the above devices, the SHG element can realize a blue light emitting laser when applied to a semiconductor laser, and has the effect of improving the storage density of an optical disk or the like and greatly increasing the storage capacity, and thus is most actively researched and developed. Is being carried out.

In order to obtain a highly efficient material for this SHG element, first of all, it is necessary that the molecular hyperpolarizability β which is a nonlinear optical constant per organic molecule is large. Second, it is important that the molecules are arranged so as to reinforce the nonlinear optical effect of each molecule. The second point is particularly important. Even if a molecule has a large hyperpolarizability, if the arrangement of molecules has a center of symmetry, the nonlinear optical effects from each molecule cancel each other out and become a material. The total nonlinear optical constant becomes zero.

The guideline for obtaining such a material is to prepare a single crystal of a noncentrosymmetric organic low-molecular compound,
Alternatively, it is possible to form an oriented thin film, but the latter is considered to be extremely effective from the viewpoint of application to devices.

As a powerful means for producing an oriented thin film, a method for producing a Langmuir-Blodgett film,
There are methods such as organic molecular beams and vacuum deposition to produce oriented thin films.However, other than these, non-linear optically active organic low molecules are dispersed in an optically transparent polymer film to form a thin film. The method of orienting molecules by applying an external electric field to the thin film and performing a poling treatment is a relatively simple method, and is being actively studied. This method is called the poled polymer method, and the features of this method are that various transparent polymer materials can be used, that many materials can be combined, and that various dispersion methods can be used. A thin film polymer material can be produced relatively easily, which is advantageous in application to devices.

The biggest problem in the poled polymer method is that the orientation due to the electric field is relaxed with time and the characteristics are deteriorated. At present, even if the dispersed low molecules are oriented using an electric field, orientation relaxation often occurs very quickly due to the relationship with the free volume of the host polymer and the segment motion.

Various approaches have been taken to solve this problem. For example, as a method of poling, a method of using corona poling instead of contact poling is used, a polymer liquid crystal is used as a host polymer to maintain the alignment state of a low-molecular compound, and its alignment force is further utilized. Attempts have also been made to chemically bond photochromic materials to enhance the alignment force and at the same time suppress phase separation. Further, it is also performed to fix a low molecular weight compound incorporated in a host polymer by fixing it to a polymer network crosslinked by two bonds. In addition, by using a non-linear optically active epoxy polymer as the host polymer itself, cross-linking reaction can be suppressed and relaxation can be suppressed and at the same time a high non-linear optical constant can be obtained, or a spontaneous polarization of a ferroelectric material can be utilized. Attempts are being made.

[0009]

As an example of using this ferroelectric material, one using polyvinylidene fluoride (hereinafter referred to as PVDF) as a host polymer is known. By subjecting PVDF to a poling treatment, the dipoles are oriented and spontaneous polarization is developed to become a ferroelectric substance.
This spontaneous polarization has the effect of orienting the nonlinear optically active organic material dispersed in the host polymer and maintaining the orientation stable over time. In addition, the host polymer itself has the effect of becoming nonlinear optical activity. However, PVDF itself is not suitable for use as a non-linear optical material in that it becomes opaque because of its large light scattering due to microcrystallization (PNPrasad and DRUlrich). Hen, P. pantelis
Et al., "Nonlinear Optics and Conducting Polymers," Plenum Press, New York and London, p.229 (1987).

As described above, PVDF is used as the host polymer.
When used, it has the effect of stably maintaining the orientation of the organic material introduced as a guest by spontaneous polarization, and since the host polymer itself is nonlinear optical activity, it is possible to obtain a material with a large nonlinear optical constant. However, the conventional method is not suitable as a nonlinear optical material because the material becomes opaque.

The present invention has been made in view of the above problems, and an object of the present invention is to obtain an organic nonlinear optical material having stable and large nonlinear optical characteristics and high transparency in the visible wavelength range.

Another object of the present invention is to obtain a non-linear optical device such as a wavelength conversion element or a light modulation element using the above non-linear optical material.

[0013]

An organic nonlinear optical material according to the present invention is a host polymer produced by melt-kneading PVDF and an acrylic polymer, quenching the melted state, and then heat-treating the mixture. The organic material in a host polymer in which a second-order nonlinear optically active organic material is introduced and dispersed by mixing or chemical bonding is oriented by an electric field application method.

Further, the organic nonlinear optical material is a nonlinear optical device.

[0015]

In the present invention, since the host polymer is a ferroelectric material having spontaneous polarization, it is possible to stably maintain the orientation of the nonlinear optically active organic material introduced as a guest molecule.

By melting and kneading a predetermined ratio of PVDF and acrylic polymer in the host polymer, quenching and heat treatment, PVDF which is normally opaque in the visible wavelength range can be obtained in a transparent state.

Further, by using this organic nonlinear optical material,
It is possible to obtain a device such as a wavelength conversion element or a light modulation element having good characteristics.

[0018]

EXAMPLES The present invention will be described below with reference to examples.

When PVDF and acrylic polymer mixed in a predetermined ratio are melted and kneaded with each other by melt-kneading at about 200 ° C., and the resin composition in a molten state is rapidly cooled with a cooling medium such as water, dry ice or liquid nitrogen. , PVD
The crystal growth of F is limited by the acrylic polymer that is well compatible with PVDF, and a resin composition with low crystallinity is obtained. When the obtained resin composition is heat treated,
Crystallization of the resin composition occurs in the presence of the acrylic polymer, and the resin composition exhibits an I-type or β-type crystal structure. As the heat treatment, a method of heating at 120 ° C. for 855 hours or more in a nitrogen gas atmosphere is preferable.

As the PVDF, a known or commercially available polymer containing vinylidene fluoride as a main component can be used. For example, a vinylidene fluoride homopolymer, a vinylidene fluoride-tetrafluoroethylene copolymer, a vinylidene fluoride-trifluoroethylene copolymer, or the like is used. As the PVDF, there is no problem even if a material mixed with an additive is used as long as the properties of the polymer are not deteriorated.

As the acrylic polymer, known or commercially available polymers containing methyl acrylate or ethyl acrylate as a main component can be used. For example, a homopolymer of methyl methacrylate, a homopolymer of ethyl acrylate, a copolymer of methyl acrylate and ethyl acrylate, etc. are used. Among these, polymethylmethacrylate is preferable because it exhibits excellent compatibility with PVDF. As the acrylic polymer, there is no problem even if a material mixed with an additive is used as long as the characteristics of the polymer are not deteriorated.

The ratio of PVDF to acrylic polymer is preferably 70/30 to 90/10 by weight. PVD
When F is less than 70/30 or more than 90/10, PVDF has a type II crystal form, and as a result, it tends to become opaque.

A secondary non-linear optically active organic material is introduced and dispersed in the host polymer (resin composition) obtained as described above. As a method of introducing and dispersing, a method of mixing and dispersing the organic material at the time of melt-kneading PVDF and an acrylic polymer, producing a host polymer film, and diffusing it by immersing it in a solution or a melt in which the organic material is dissolved And a method of chemically bonding the organic material to the monomer of the acrylic polymer in advance.

The second-order nonlinear optically active organic material is preferably a compound having π-conjugation and having a molecular structure having no center of symmetry. Examples thereof include, but are not limited to, a compound in which a nitro group or an amino group is bonded to an aromatic ring or a heteroaromatic ring so as not to have a symmetry center.

The ratio of the organic material to the host polymer is not particularly limited as long as the organic material is uniformly dispersed in the host polymer and does not become opaque.

By aligning the non-linearly optically active organic material introduced into the host polymer as described above in the uniaxial direction by the electric field application method, a high-performance non-linear optical material is obtained. A contact poling method, a corona poling method, or the like is used as the electric field applying method. In this poling method, a polymer film is heated up to around a glass transition point and an electric field is applied to the dispersed organic material, which is made easy to move and is oriented in the direction of the electric field.

A device using the organic nonlinear optical material of the present invention as described above is the nonlinear optical device of the present invention. Specific examples thereof include a wavelength conversion element, an electro-optical modulation element, an optical integrated element, and a high speed switching element.

Since the organic nonlinear optical material of the present invention is uniaxially oriented in the direction perpendicular to the film surface, when it is used as a device, a waveguide type is a good measure for utilizing the characteristics.

The present invention will be described below with reference to specific examples. Basic sample: Acrypet VHK (trade name, Mitsubishi Rayon Co., Ltd.), which is an acrylic resin, 20 parts (weight part, the same applies hereinafter)
After melting and kneading 80 parts of KF polymer # 1100 (trade name, Kureha Chemical Industry Co., Ltd.), which is a vinylidene fluoride resin, with a single-screw extruder (L / D = 25) with a screw diameter of 35 mm, a cylinder is used. The mixture was melt-kneaded at a temperature of 200 ° C. and a rotation speed of 80 rpm and cooled and ground to obtain pellets of the kneaded product. Next,
Put the required amount between the pellets in a metal mirror plate whose thickness is adjusted with a spacer, and press and melt for 5 minutes with a hot press at 200 ° C and a pressure of 50 megapascals, then hold the resin between the metal plates. , Quickly cooled in liquid nitrogen. The film thickness is about 50 μm. This sample is used as a basic sample.

Reference Example 1 A basic sample was placed in a hot air circulation furnace at 120 ° C. and heat-treated for 2 hours in a nitrogen stream. When the obtained sample was analyzed by an X-ray diffractometer and infrared spectroscopy, it was confirmed that PVDF type I crystal was produced, and a highly transparent film was obtained. Aluminum electrodes were formed on both surfaces of this sample by vacuum vapor deposition, and then poling was carried out at 80 ° C. for 1 hour under a nitrogen stream. The poling electric field is 0.5 MV / cm. This sample is referred to as sample 1.

[Example 1] In the molten state at the time of preparing a basic sample, a second-order nonlinear optically active 4-dimethylamino-
4'-nitrostilbene (hereinafter referred to as DANS)
A sample containing DANS was obtained by adding 4% by weight. This sample was heat-treated in the same manner as in Reference Example 1 and was subjected to a poling treatment at 0.5 MV / cm to obtain a sample 2.

Reference Example 2 Sample 3 was prepared in the same manner as in Reference Example 1 except that the poling electric field was 0.8 MV / cm.
And

Example 2 A film obtained by immersing a basic sample in a boiling propanol solution in which DANS was dissolved at 0.0078 mol / L for 4 hours was heat treated in the same manner as in Reference Example 1 to obtain 0.8 MV /
The sample poled by cm is referred to as sample 4. Measurement of absorption spectrum: FIG. 1 shows the absorption spectrum of Sample 1. It shows good transparency over the visible wavelength range. Measurement of SHG characteristics: The SHG characteristics of each obtained sample were measured by the maker fringe method. The maker fringe method is a method used to evaluate the nonlinear optical constant of a thin film material, and the constant is determined by comparison with a standard sample (quartz single crystal). Further, the tensor component of the non-linear optical constant can be determined by rotating the sample with respect to the incident light or by combining the incident light and the emitted SH light with P polarization or S polarization, respectively.

The experimental system used in this measurement is shown in FIG. YA
The laser light with a wavelength of 1.06 μm emitted from the G laser 1 has a polarizer 2
After being linearly polarized by the lens 3, the light is condensed by the lens 3 and is irradiated on the sample thin film 5 on the rotary stage 4. Second harmonics are generated in the sample, the incident light is removed by the filter 6, the light amount is adjusted to an appropriate amount, and only the SH light of the desired polarization is extracted by the polarizer 7, and the photomultiplier tube 8
Detected by. In the figure, 9 is a boxcar integrator, 10
Is the controller. The SHG characteristics of the sample were measured by removing the electrode deposited on the sample.

Table 1 shows the measured nonlinear optical constants of Samples 1 to 4. As can be seen from the measured values of Sample 1 and Sample 3, the host polymer itself exhibits a large nonlinear optical constant. Also, it can be seen that the larger the poling electric field, the larger the nonlinear constant. Further, from the comparison between sample 1 and sample 2 and the comparison between sample 3 and sample 4, it can be seen that the introduction of DANS increases the nonlinear optical constant.

It was found that the SHG characteristics did not change even after 2 to 3 weeks from the preparation of the sample and were stable.

[0037]

[Table 1] [Embodiment 3] FIG. 3 is a view showing the structure of a waveguide type wavelength conversion element which is an embodiment of the nonlinear optical device of the present invention.
11 is the incident fundamental wave, 12 is the sample thin film, 13 is the electrode, 14 is the substrate,
15 is the emitted SH light. Here, a glass substrate was used as the substrate 14, an ITO transparent electrode was used as the electrode 13, and a non-linear optical material thin film having the same composition as the sample 4 of Example 2 was provided as the sample thin film 12. For poling, an aluminum vapor deposition film formed on the sample thin film 12 was used as an electrode, an electric field of 0.8 MV / cm was applied between the electrode and the transparent electrode 13, and the electrode was removed after the poling was completed.

When a laser beam of 1.06 μm as a fundamental wave 11 is incident on this waveguide type wavelength conversion element, it is converted into SH light.
Generation of 532 nm was confirmed.

[Embodiment 4] FIG. 4 is a diagram showing the structure of a waveguide type optical modulator which is an embodiment of the nonlinear optical device of the present invention. Reference numeral 12 is a sample thin film, 13 is an electrode, 14 is a substrate, 16 is a buffer layer, 17 is a modulation voltage applying electrode, and 18 and 19 are coupling prisms for incidence and emission, respectively. Here, as in the third embodiment, a glass substrate is used as the substrate 14 and the electrodes are
An ITO transparent electrode was used for 13, and a non-linear optical thin film having the same composition as that of Sample 4 of Example 2 was provided as the sample thin film 12.

The buffer layer 16 is a layer for reducing the propagation loss of the light guided in the sample thin film 12, and is not always necessary. However, to work as a buffer layer,
It is necessary that the refractive index is smaller than that of the sample thin film 12. PVDF / PMMA (80/2 used as sample thin film 12
0) has a refractive index of 1.44, and a fluororesin can be cited as a material having a smaller refractive index. In this example, CYTOP (refractive index 1.34) manufactured by Asahi Glass Co., Ltd. was used.

The poling of the sample thin film 12 was performed in the same manner as in Example 3 using the transparent electrode 13 and the modulation voltage applying electrode 17 provided on the buffer layer 16 at an electric field of 0.8 MV / cm.

The incident light 20 polarized by the polarizer 21 at 45 ° was introduced and propagated through the waveguide type light modulation element through the entrance coupling prism 18. The light propagating in the sample thin film 12 was modulated by the electro-optical effect caused by applying the modulation voltage 24 to the modulation voltage applying electrode 17.
Specifically, since the effective refractive indices of the TE polarization component and the TM polarization component of the guided light change, the polarization of the output light extracted through the output coupling prism 19 changes. The emitted light 23 of only the modulation component can be taken out by the polarizer 22 on the incident side and the analyzer 22 set in the crossed Nicol arrangement. He− of 632.8 nm as incident light 20
When Ne laser light was introduced and a modulation voltage 24 was applied,
It was confirmed that the light intensity was modulated.

[0043]

As described above, the organic non-linear optical material according to the present invention is melt-kneaded with PVDF and an acrylic polymer as a host polymer into which a non-linearly optically active organic material is introduced, and is rapidly cooled and heat-treated from the molten state. Since a ferroelectric material with excellent transparency and large spontaneous polarization is used, the orientation of the introduced organic material can be stably maintained, and it has the effect of becoming a nonlinear optical material with excellent transparency. Furthermore, the host polymer itself Exhibits a non-linear optical characteristic, so that the material has a high non-linear optical constant.

The non-linear optical device of the present invention using the above-mentioned organic non-linear optical material is a non-linear optical device having a large non-linear optical constant and stability and a high response speed.

[Brief description of drawings]

FIG. 1 is an absorption spectrum of Sample 1 obtained in Reference Example 1.

[FIG. 2] SH for measuring the nonlinear optical constants used in the examples
It is an optical-path figure of the measuring system of G maker fringe method.

FIG. 3 is an explanatory diagram of a structure of a waveguide type wavelength conversion element according to a third embodiment.

FIG. 4 is an explanatory diagram of a structure of a waveguide type optical modulator of Example 4.

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[Procedure amendment]

[Submission date] January 24, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

[0009]

As an example of using this ferroelectric material, one using polyvinylidene fluoride (hereinafter referred to as PVDF) as a host polymer is known. By subjecting PVDF to a poling treatment, the dipoles are oriented and spontaneous polarization is developed to become a ferroelectric substance. This spontaneous polarization has the effect of orienting the nonlinear optically active organic material dispersed in the host polymer and maintaining the orientation stable over time. In addition, the host polymer itself has the effect of becoming nonlinear optical activity. However,
When PVDF is used alone as the host polymer,
Because it is a crystalline polymer, it does not crystallize.
As a result, light scattering occurs and becomes opaque.
U Therefore, as it is, it is unsuitable for use as a nonlinear optical material (PNPrasa (PNPrasa
d) and DRUlrich
Edited by P. pantelis et al., “Nonlinear Optics and Conducting Polymers,” Plenum Pres.
ss) New York and London, p.229 (198
7)).

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

By melting and kneading a predetermined ratio of PVDF and acrylic polymer in the host polymer, quenching and heat treatment, PVDF which is normally opaque due to light scattering can be obtained in a transparent state.

Claims (2)

[Claims] 1. A host polymer produced by melt-kneading polyvinylidene fluoride and an acrylic polymer, quenching the melted state, and then heat-treating the mixture, wherein a second-order nonlinear optically active organic material is mixed or mixed. An organic non-linear optical material, characterized in that the organic material in a host polymer introduced and dispersed by a chemical bond is oriented by an electric field application method. 2. A nonlinear optical device using the organic nonlinear optical material according to claim 1.